He pointed out that my best work always came when I was having fun. When I was loose. When I wasn't letting things get to me. He pointed out a few campaigns where he knew I had had fun producing them. They were the ones that had won awards. By contrast, the assignments that I'd struggled with were the ones where I was working too hard, second-guessing the client, and fed-up with too much feedback.
None of that was news to me. But I realized for the first time how apparent my enthusiasm (and lack, thereof) was to others.
My point: Have fun. You'll work better that way. If you're not having fun, find a way to make it fun. Sure, that's easier said than done. But it's better than complaining, moping and still having to produce something.